1. Field of the Invention
The present invention relates to a vibratory flow meter, and more particularly, to a vibratory flow meter and method for determining viscosity in a flow material.
2. Statement of the Problem
Flow meters are widely used to measure the characteristics of flowing fluids, including gases and liquids. The characteristics can include a mass flow rate and a density, for example. The characteristics can further include a viscosity of the flow fluid. Viscosity is commonly defined as a measure of the resistance of a fluid to deformation under a shear stress. It can also be thought of as a resistance to flow or a fluid friction.
A viscosity measurement may be needed in many situations. A viscosity measurement may be needed when the end product is desired to have a predetermined viscosity. Examples are motor oils and other lubricants, where the viscosity of a produced or refined petroleum product may be required to fall within a predefined viscosity range. A viscosity measurement may be needed or required in the production of syrups and other food products. A viscosity may be needed in order to control or characterize an industrial process.
Viscometers exist. One type of viscometer is a rotation viscometer, wherein a body of some sort is rotated in a fluid. The force required to perform the rotation is measured and is used to derive the viscosity measurement. The rotation viscometer has drawbacks, however. Foremost is that the fluid sample must be removed from the process pipeline in order to measure its viscosity. Also, various fluids may exhibit a great range in viscosity as much as four orders of magnitude in some cases. Therefore, a rotation viscometer may perform well at some viscosities but may not be best suited for measuring viscosity of certain fluids and may not perform well at higher or lower viscosities. A rotation viscometer may present problems in applications where the device needs to be cleaned and cannot retain the flow material, such as in the food industry or in the chemical or semiconductor industries.
Coriolis meters and vibratory densimeters operate by vibrating one or more flowtubes that are conducting a flow material. Such vibratory flow meters advantageously do not restrict a flow during operation. In addition, such vibratory flow meters comprise essentially smooth and uninterrupted conduits that are easy to empty and easy to clean. This offers advantages in many flow measuring environments.